Which type of matter in the nervous system is myelinated?

The correct answer is indeed white matter. In the nervous system, white matter is distinguished by its myelinated axons, which are the long, slender projections of nerve cells that transmit electrical signals. The myelin sheath, composed of fatty substances, insulates these axons and increases the speed at which nerve impulses can travel. This is crucial for efficient communication between different parts of the nervous system.

In contrast, grey matter primarily consists of neuronal cell bodies, dendrites, and unmyelinated axons. It is where much of the processing of information occurs, particularly in areas like the cerebral cortex and spinal cord. Synaptic matter refers to the areas of synaptic connections between neurons and is not a recognized classification of matter like grey or white matter. Neuropil is a dense network of interwoven axons, dendrites, and glial cells found in grey matter, further emphasizing that it lacks the myelination characteristics found in white matter.

Thus, the primary distinction that makes white matter the correct choice lies in its myelinated axons, which facilitate faster signal transmission necessary for the nervous system's overall function.